Apparatus and methods for generating water in a fuel cell system

ABSTRACT

Apparatus and methods for the generation of water in a direct oxidation fuel cell. Water, in addition to carbon dioxide and heat, is produced when carbonaceous fuel or fuel solution is oxidized in the presence of air and a suitable catalyst. This oxidation reaction is performed on a surface that allows for the introduction of oxygen in the presence of a catalyst. Water produced can then be directly added to the fuel solution thereby diluting the fuel solution to a desired concentration, or may be separately and then later added to fuel solution for the normal fuel cell operations depending on the permeability of the membrane to water.

FIELD OF THE INVENTION

The present invention relates generally to the field of fuel cells and,more specifically, to a direct methanol fuel cell system in which theneed to store water in the system or fuel supply is minimized oreliminated through the provision of a water generator.

BACKGROUND INFORMATION

Fuel cells are devices in which an electrochemical reaction is used togenerate electricity. A variety of materials may be suited for use as afuel depending upon the materials chosen for the components of the cell.Organic materials, such as methanol or natural gas, are attractivechoices for fuel due to the their high specific energy.

Fuel cell systems may be divided into “reformer-based” systems (i.e.,those in which the fuel is processed in some fashion to extract hydrogenfrom the fuel before it is introduced into the fuel cell system) or“direct oxidation” systems in which the fuel is fed directly into thecell without the need for separate internal or external processing. Mostcurrently available fuel cells are reformer-based fuel cell systems.However, because fuel-processing is complex, expensive and requiressignificant volume, reformer based systems are presently limited tocomparatively high power applications.

Direct oxidation fuel cell systems may be better suited for a number ofapplications in smaller mobile devices (e.g., mobile phones, handheldand laptop computers), as well as in some larger applications.Typically, in direct oxidation fuel cells, a carbonaceous liquid fuel inan aqueous solution (typically aqueous methanol) is applied to the anodeface of a membrane electrode assembly (MEA). The MEA contains aprotonically-conductive, but electronically non-conductive membrane(PCM). Typically, a catalyst which enables direct oxidation of the fuelon the anode is disposed on the surface of the PCM (or is otherwisepresent in the anode chamber of the fuel cell). Diffusion layers aretypically in contact with each of the catalyzed anode and cathode facesof the PCM to facilitate the introduction of reactants and removal ofproducts of the reaction from the PCM, and also serve to conductelectrons. Protons (from hydrogen found in the fuel and water moleculesinvolved in the anodic reaction) are separated from the electrons. Theprotons migrate through the PCM, which is impermeable to the electrons.The electrons thus seek a different path to reunite with the protons andoxygen molecules involved in the cathodic reaction and travel through aload, providing electrical power.

One example of a direct oxidation fuel cell system is a direct methanolfuel cell system or DMFC system. In a DMFC system, methanol in anaqueous solution is used as fuel (the “fuel mixture”), and oxygen,preferably from ambient air, is used as the oxidizing agent. There aretwo fundamental half reactions that occur in a DMFC which allow a DMFCsystem to provide electricity to power consuming devices: the anodicdisassociation of the methanol and water fuel mixture into CO₂, protons,and electrons; and the cathodic combination of protons, electrons andoxygen into water. The overall reaction may be limited by the failure ofeither of these reactions to proceed to completion at an acceptable rate(more specifically, failure to oxidize the fuel mixture will limit thecathodic generation of water, and vice versa).

Fuel cells and fuel cell systems have been the subject of intensifiedrecent development because of their ability to efficiently convert theenergy in carbonaceous fuels into electric power while emittingcomparatively low levels of environmentally harmful substances. Theadaptation of fuel cell systems to mobile uses, however, is notstraightforward because of the technical difficulties associated withreforming most carbonaceous fuels in a simple, cost effective manner,and within acceptable form factors and volume limits. Further, a safeand efficient storage means for substantially pure hydrogen (which is agas under the relevant operating conditions), presents a challengebecause hydrogen gas must be stored at high pressure and at cryogenictemperatures or in heavy adsorption matrices in order to achieve usefulenergy densities. It has been found, however, that a compact means forstoring hydrogen is in a hydrogen rich compound with relatively weakchemical bonds, such as methanol or an aqueous methanol solution (and tosome extent, ethanol, and other carbonaceous fluids or aqueous solutionsthereof).

In particular, DMFCs are being developed for commercial production foruse in portable electronic devices. Thus, the DMFC system, including thefuel cell, and the components may be fabricated using materials that notonly optimize the electricity-generating reactions, but which are alsocost effective, and allow the fuel cell system to fit demanding formfactors. Furthermore, the manufacturing process associated with thosematerials should not be prohibitive in terms of labor intensity cost.

Typical DMFC systems include a fuel source, fluid and effluentmanagement systems, and a direct methanol fuel cell (“fuel cell”). Thefuel cell typically consists of a housing, and a membrane electrodeassembly (“MEA”) disposed within the housing.

A typical MEA includes a centrally disposed protonically conductive,electronically non-conductive membrane (“PCM”). One example of acommercially available PCM is Nafion ® a registered trademark of E.I.Dupont de Nours and Company, a cation exchange membrane comprised ofperfluorosulfonic acid, in a variety of thicknesses and equivalentweights. The PCM is typically coated on each face with anelectrocatalyst such as platinum, or platinum/ruthenium mixtures oralloy particles. On either face of the catalyst coated PCM, theelectrode assembly typically includes a diffusion layer. The diffusionlayers function to evenly distribute the liquid fuel mixture across thecatalyzed anode face of the PCM, or the gaseous oxygen from air or othersource across the catalyzed cathode face of the PCM. In addition, flowfield plates are often placed on the aspect of each diffusion layer thatis not in contact with the catalyst-coated PCM. The flow field platesmay function to provide mass transport of the reactants and by productsof the electrochemical reactions and also have a current collectionfunctionality to collect and conduct electrons through the load.

The direct oxidation fuel cell based on oxidation of methanol requireswater and methanol to be present together at the anode catalyst in orderfor the oxidation half reaction of methanol to proceed to completion.However, in an energy conversion device based upon DMFC technology, fora given energy content, the size of the device is readily reduced bycarrying only methanol in the fuel reservoir as opposed to amethanol-water solution. In some architectures, a portion of the waterrequired will be present in the anode chamber, or may be recirculatedfrom the cathode aspect of the DMFC, however, it may be necessary togenerate additional water under some conditions. In other words, thevolumetric energy density of the device can be maximized by reducing theamount of water stored in the methanol-water solution within the DMFC.This would require a method of water production within the device inorder to drive the anodic half reaction to completion.

It is thus an object of the invention to provide a water generator thatprovides water for diluting the methanol supplied to the DMFC whileincreasing the volumetric energy returns of the fuel cell system overits lifetime.

SUMMARY OF THE INVENTION

In brief summary, the present invention provides a direct methanol fuelcell system in which water may be generated from methanol or othersuitable fuel, thereby eliminating the need to store water, reducing thesize of the fuel supply required to provide power, and increasing theenergy yield by unit volume. In a preferred embodiment, the presentinvention uses a method of production of water based upon acatalytically facilitated reaction in which methanol is oxidized in thepresence of oxygen to produce water, carbon dioxide and heat. Unlike thereaction that occurs in the direct oxidation fuel cells in which a fuelor fuel solution, water and oxygen are reacted in two separate halfreactions, here oxygen reacts directly with the fuel or fuel solution inthe presence of a suitable catalyst, producing water, carbon dioxide andsome heat rather than electrical energy.

In the preferred embodiment, the reaction of carbonaceous fuel or fuelsolution and oxygen to produce water, carbon dioxide and heat occursspontaneously under relevant conditions, in the presence of a suitablecatalyst, including, but not limited to platinum and platinum-ruthenium,without the need for external activation energy to be applied.Therefore, the only loss to the fuel cell system is the efficiency lossdue to the oxidation of the fuel to generate water, rather thanelectricity.

A direct oxidation fuel cell (“DOFC”) which uses the present inventionmay be configured such that a water generator is coupled to a flow paththat connects the fuel source and anode chamber of the DOFC, or a flowpath that connects the fuel source to the anode chamber, or ispositioned along the path between the fuel source and the anode chamber.A pump, valve, or other passive means may be used to supply methanol tothe water generator. In the embodiments summarized below, thecarbonaceous fuel can be a pure fuel, a solution of fuel and water, or amixture of fuels or fuel-water solutions.

The invention consists of a method of generating water for use within adirect oxidation fuel cell by introducing the fuel to a catalyzedsurface or substrate within the direct oxidation fuel cell system in thepresence of oxygen. This causes said fuel to be oxidized, resulting inthe generation of water, allowing for the dilution of fuel within thefuel cell system and preventing said fuel from passing through the PCMwithout contributing to the electricity-generating reactions (fuelcrossover).

In a first embodiment, the water generator may be provided by a materialwhich is permeable to a carbonaceous fuel suitable for use in the fuelcell system, and treated on the outside surface with a catalyst (e.g.platinum or platinum-ruthenium) that activates the oxidation of fuel inthe presence of oxygen. Preferably, the material of this embodiment istubular and fluted in shape. In this embodiment, it is preferred thatthe carbonaceous fuel is introduced to the inside of a tube fabricatedfrom the fuel-permeable, substantially gas-impermeable material. Some ofthe fuel permeates the material and reacts with oxygen on the catalyston the outside of the tube, producing carbon dioxide, water and heat. Atleast one other portion of the tube fabricated from the fuel-permeablematerial may be left catalyst free so that water can diffuse back intothe inside of the tube. Another aspect of this embodiment is to enclosethe outside of the tube with a liquid-impermeable, gas-permeablematerial so that the carbon dioxide produced by the oxidation of thefuel may diffuse through the liquid-impermeable, gas-permeable material,leaving the space between the materials as a collection area for thewater, or encouraging the water to be transported into the tubefabricated from the fuel-permeable, gas-impermeable material, bycreating a pressure or concentration gradient between theliquid-impermeable, gas-permeable material and the tube.

In a second embodiment, the water generator may be provided by agas-permeable, liquid-impermeable material. In the preferred embodiment,the gas-permeable liquid-impermeable material is in the shape of afluted tube and coated on the inside surface with a catalyst capable ofpromoting oxidation of a carbonaceous fuel in the presence of oxygen.The carbonaceous fuel is introduced to the inside of the tube fashionedfrom the gas-permeable, liquid-impermeable material, and as air diffusesinside through the gas-permeable, liquid-impermeable material, theoxidation reaction occurs on the inside of the tube fashioned from thegas-permeable, liquid-impermeable material, producing water, carbondioxide and heat. A portion of the material is left uncatalyzed so thatexcess air and carbon dioxide may diffuse to the outside of the tuberesulting in liquid water being collected, substantially gas free, onthe inside of the gas-permeable, liquid-impermeable material. Thoseskilled in the art will recognize that the materials described hereinfor the purpose of transporting liquids or gases may consist of formedmembranes, extruded materials, or using other methods well known tothose skilled in the art.

In a third embodiment, the water generator is a membrane electrodeassembly (MEA) configured for direct oxidation of a carbonaceous fuel,where electricity generated can be harnessed and delivered to theapplication, and in which the MEA can also be used to generate water foruse within the fuel cell system. When water generation is desired,oxygen is used to directly oxidize the carbonaceous fuel in the presenceof a catalyst found at the anode of the MEA, producing carbon dioxide,heat and water.

There are several key benefits of this invention. The first is that thefuel solution (e.g. methanol or an aqueous methanol solution) can bequickly diluted by adding water to the fuel mixture prior to theintroduction of fuel into the anode chamber, or adding water into thefuel mixture, thus minimizing fuel crossover. Losses due to thegeneration of water by intentionally oxidizing fuel, will be less thanthe losses due to the fuel cross-over. Secondly, this inventionminimizes or eliminates the need to carry a dilute, and therefore morevoluminous, fuel mixture into the fuel cell system. This makes moreefficient use of the volume of the fuel cell, as well as providing theability to carry a fuel supply that is more concentrated than ispresently practical. Thirdly, eliminating the need to carry water maysimplify the system design by providing a system with fewer conduits andfluidic connections. This may simplify manufacturing as well. Inaddition, because the chemical conversion to water is relativelyefficient, the concentration of the fuel can be easily controlled bycontrolling the amount of fuel that is oxidized for the purpose ofgenerating water. Those skilled in the art will also recognize that thereactions create heat, which may also be useful from time to time.

Those skilled in the art will recognize that this invention may beimplemented in fuel cell systems consisting of one or more fuel cells,including systems where a plurality of cells are “stacked” in order tomeet the power profiles of the application to which electricity is beingsupplied.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention description below refers to the accompanying drawings, ofwhich:

FIG. 1 is a block diagram of a direct fuel cell system known in theprior art;

FIG. 2 is a block diagram of a direct oxidation fuel cell with anattached water generator constructed in accordance with a preferredembodiment of the present invention;

FIG. 3 is a perspective of a first embodiment of a water generator ofthe type shown in FIG. 2;

FIG. 4 is a perspective of the water generator of FIG. 3 with agas-permeable material enclosing the material permeable by a desiredcarbonaceous fuel;

FIG. 5 is a perspective of a second embodiment of a water generator ofthe type shown in FIG. 2;

FIG. 6 is a perspective of a third embodiment of a water generator ofthe type shown in FIG. 2;

FIG. 7 is a block diagram of an alternative embodiment of a directoxidation fuel cell with an attached water generator, which may use anyof the water generators of FIGS. 3-6; and

FIG. 8 is a block diagram of a second alternative embodiment of a directoxidation fuel cell with an attached water generator, which may use anyof the water generators of FIGS. 3-6.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

A direct oxidation fuel system 2 is schematically illustrated in FIG. 1.The fuel cell system 2 includes a direct oxidation fuel cell, which maybe a direct methanol fuel cell 3 (“DMFC”), for example. For purposes ofillustration we herein describe an illustrative embodiment of theinvention with DMFC 3, or DMFC system with the fuel substance beingmethanol or an aqueous methanol solution. It should be understood,however, that it is within the scope of the present invention that otherfuels such as ethanol, or combinations thereof and aqueous solutionsthereof, and other carbonaceous fuels amenable to use in DMFC systemsmay be used. It should be further understood that the invention isapplicable to any fuel cell system where it is preferable to introducewater to the reactants in order to facilitate the operation of the fuelcell system, and not simply those that are similar to those set forth inFIG. 1.

The system 2, including the DMFC 3, has a fuel delivery system todeliver fuel from fuel source 4. The DMFC 3 includes a housing 5 thatencloses a membrane electrode assembly 6 (MEA). MEA 6 incorporatesprotonically conductive, electronically non-conductive, membrane (PCM)7. PCM 7 has an anode face 8 and cathode face 9, each of which may becoated with a catalyst, including but not limited to platinum or a blendof platinum and ruthenium. Diffusion layers are typically provided andin intimate contact with the catalyzed faces of each of the anode andcathode aspects of the PCM, though the invention is not limited tosystems that require diffusion layers. The portion of DMFC 3 defined bythe housing 5 and the anode face of the PCM is referred to herein as theanode chamber 10. The portion of DMFC 3 defined by the housing 5 and thecathode face of the PCM 7 is referred to herein as the cathode chamber20. Those skilled in the art will recognize that the catalyst may beapplied to the PCM by applying a suspension containing the catalyst toPCM. As used herein the terms “anode face” and “cathode face” may referto the catalyzed faces of the PCM, and shall include any residualcatalyst materials that may remain on the surface of the PCM as theresult of such application.

As will be understood by those skilled in the art,electricity-generating reactions occur when a fuel substance isintroduced to the anode face 8, and oxygen, usually in the form ofambient air, is introduced to the cathode face 9. More specifically, acarbonaceous fuel substance from fuel source 4 is delivered by pump 11to the anode chamber 10 of the DMFC 3. The fuel mixture passes throughchannels in the flow field plate, and/or a diffusion layer, and isultimately presented to the anode face of the PCM 8. Catalysts on themembrane surface (or which are otherwise present within the MEA) enablethe anodic oxidation of the carbonaceous fuel on the anode face 8,separating hydrogen protons and electrons from the fuel and watermolecules of the fuel mixture. Upon the closing of a circuit, protonspass through PCM 7, which is impermeable to the electrons. The electronsthus seek a different path to reunite with the protons, and travelthrough a load 13 of an external circuit, thus providing electricalpower to the load. So long as the reactions continue, a current ismaintained through the external circuit. Direct oxidation fuel cellsproduce water (H₂O) and carbon dioxide (CO₂) as byproducts of thereaction. The water collector 14 acts as a storage unit for waterproduced. This water can be later directed to the pump 11 via a flowpath 19.

FIG. 2 illustrates a direct oxidation fuel cell 24 and a water generator23, which, in a preferred embodiment, can be implemented with a DMFCsystem 21. Water generator 23 is coupled to anode chamber 26 by aconduit 27. Conduits 29 and 30 couple a fuel source 22 to watergenerator 23 and anode chamber 26, respectively. Operation of the watergenerator 23 is controlled by the operation of valve 20, which managesthe flow of fuel or fuel solution into the water generator 23. Thedetailed construction of various preferred embodiments of the watergenerator 23 may be understood with reference to FIGS. 3-6.

Water generator 23 is comprised of at least one substrate or surface 231that is treated with a catalyst 232. Said substrate 231 does not reactwith, or interfere with the catalytic oxidation of methanol, or otherappropriate fuel, in the presence of oxygen, and does not react with thefuel or products of said oxidation. Said surface 231 may be disposedwithin a housing (not shown), which may, but need not, have valves orother components (not shown) that control the introduction of fuel andair, as well as the distribution of catalytically generated water andcarbon dioxide.

With reference to FIG. 3, a fuel-permeable, substantiallygas-impermeable material 32, including but not limited to uncatalyzedNafion®, is provided in the shape of a tube. The tube is preferably, butdoes not need to be, in a fluted configuration to provide greatersurface area for the catalytic oxidation of the fuel. A first portion 33of the outer surface 36 of the fuel-permeable, substantiallygas-impermeable material 32 is treated with a catalyst 35 capable ofpromoting the oxidation of the fuel or fuel solution in the presence ofair, including, but not limited to platinum or a blend of platinum andruthenium. In the preferred embodiment, the catalyst is applied to atleast one portion of the outer surface 36 of the fuel-permeable,substantially gas-impermeable material 32. At least one other portion ofthe fuel-permeable, substantially gas-impermeable material 32 remainsuncatalyzed, such as portion 34. In this embodiment, the fuel or fuelsolution is introduced to the inside of the fuel-permeable,substantially gas-impermeable material 32 at one end 37. Some of thefuel permeates the fuel-permeable, substantially gas-impermeablematerial 32 to the outer surface 36. Oxygen, preferably from ambient airpresent on the outside of the fuel-permeable, substantiallygas-impermeable material 32, or which is otherwise provided access tothe catalyst, then reacts with fuel or fuel solution in the presence ofthe catalyst 35 producing carbon dioxide, water and heat. Water or adilute fuel solution may diffuse back into fuel-permeable, substantiallygas-impermeable material 32 through the uncatalyzed portion 34, and to alesser extent through the portion that has been treated with catalyst.Those skilled in the art will recognize that the materials describedherein for the construction of the water generator may consist of formedmembranes, extruded materials, or other means well known to thoseskilled in the art.

FIG. 4 shows an alternative embodiment of the water generator 23 (seeFIG. 2). A gas-permeable, liquid-impermeable membrane 42 fabricated fromappropriate materials, including, but not limited to expanded PTFEavailable from Zeus Inc. and other commercial manufacturers, encloses afuel-permeable, gas-impermeable material 43, which has been treated withcatalyst, and which is similar in construction to the embodiment shownin FIG. 3. As a result, any generated water remains on the inside ofgas-permeable, liquid-impermeable material 42, and may diffuse back intothe fuel or fuel solution passing through gas-impermeable,liquid-permeable material 43. Gas-permeable, liquid-impermeable material42 is preferably fabricated from a highly hydrophobic material that iseither in intimate contact with or that creates a very small volumebetween gas-permeable, liquid-impermeable material 42 and thefuel-permeable, gas-impermeable material 43. Such fabrication willcreate a pressure or gradient to drive water or a diluted fuel solutionback into the conduit formed by fuel-permeable, gas-impermeable material43, thus diluting the fuel mixture being delivered from the watergenerator to the anode chamber.

Alternatively, water or a dilute fuel solution may remain outside of thefuel-permeable substantially gas-impermeable material 43, and becollected at the end of the conduits formed by materials 42 and 43.Excess air and carbon dioxide permeate the gas-permeable,liquid-impermeable material 42 and are vented to the ambient environmentor used within the fuel cell system to perform work including, but notlimited to, driving a pump prior to being vented from the system. Thoseskilled in the art will recognize that it may be necessary to implementa gas/liquid separator (not shown) between the water generator 41 andthe anode chamber 26 (see FIG. 2). The gas/liquid separator ispreferably disposed between the water generator 23 (see FIG. 2) and theanode chamber 26 (see FIG. 2) or conduit 27, (see FIG. 2) into whichwater is to be introduced, in order to effectively separate thegenerated carbon dioxide and any remaining oxygen from the liquidmixture being passed through water generator 41. Such disposition of thegas/liquid separator (not shown) also allows the fuel to be introducedto the anode chamber 26 (see FIG. 2) without introducing oxygen into thecathode chamber 28 (see FIG. 2) of the direct oxidation fuel cell 24(see FIG. 2).

FIG. 5 shows a second embodiment of the invention in which a watergenerator 51 includes a gas-permeable, liquid-impermeable material 52 ina tubular shape. The tube is preferably, but does not need to be, in afluted configuration. In this embodiment, a catalyst 55 has been appliedto the inner surface 57 of the gas-permeable, liquid-impermeablematerial 52. The fuel or fuel solution is introduced to the inside ofthe gas-permeable, liquid-impermeable material 52 at one end. Airpermeates the gas-permeable, liquid-impermeable material 52 to the innersurface of the material 57. Oxygen that is available on the innersurface 57 of the material then reacts with fuel in the presence of thecatalyst 55, to produce carbon dioxide, water and heat. At least oneother portion 54 of the gas-permeable, liquid-impermeable material 52 isleft uncatalyzed so that excess air and carbon dioxide may be ventedfrom the inside of the gas-permeable, liquid-impermeable material 52. Asa result, water or a diluted fuel solution is collected gas free fromthe end of the gas-permeable, liquid-impermeable material 52 oppositethe end where fuel was introduced. Those skilled in the art willrecognize that it may be preferable to include a plug (not shown), orotherwise restrict the flow of the water or dilute fuel mixture in orderto generate sufficient backpressure to encourage gases present in saidwater generator to be removed prior to entering the anode chamber 26(see FIG. 2) of the fuel cell 24 (see FIG. 2).

FIG. 6 shows a third embodiment of the present invention in which awater generator/DMFC 61 includes a membrane electrode assembly 62 (MEA)configured for direct fuel oxidation and power generation. For purposesof illustration, and not by way of limitation, water generator/directoxidation fuel cell 61, shall be referred to as “water generator/DMFC”herein. The MEA is enclosed in a housing 73 forming an anode chamber 66between housing 73 and anode aspect of the PCM 65, and a cathode chamber67 between the housing 73 and the cathode aspect of the PCM 63. Watergenerator/DMFC 61 may be substituted for water generator 23 (see FIG.2). In a first operation mode, where no electricity is generated, airand fuel or fuel solution are introduced into the anode compartment 66via openings 69 and 70 respectively. A catalyst that promotes theoxidation of fuel has been applied to the anode face of PCM, and thusthe fuel is oxidized completely (i.e. into water and carbon dioxide)when introduced to the anode chamber 66 in the presence of oxygen.Carbon dioxide exits the housing 75 via opening 72, and is removed fromthe system while water or dilute fuel leaves via opening 71 and isintroduced to the anode chamber of a fuel cell. In the second operationmode, oxygen is prevented from entering the anode chamber 66, and wateris generated on the catalyzed cathode aspect of the PCM 63. As such, thewater generator/DMFC 61 functions essentially as a conventional directmethanol fuel cell and produces electricity, which may be used tosupport a load within the application to which electricity is beingprovided. Said water generator/DMFC 61 can be used to generate waterby: 1) introducing excess fuel (in proportion to the demand of theattached load) to a DMFC of standard design and materials; or 2)introducing fuel to a to water generator/DMFC 61 t without a load beingconnected between the anode and cathode aspects of the watergenerator/DMFC 61. By doing so, fuel crossover is promoted, and fuelthat passes through the PCM is oxidized without generating electricity,thus forming additional water in the cathode chamber 67 of the watergenerator/DMFC 61. It may be further possible to intentionally vary saidload attached to water generator/DMFC 61 periodically in order toperiodically induce fuel crossover, and resulting generation of water.Said additional water may be transported within the system (21 of FIG.2) as necessary.

FIG. 7 illustrates an alternative embodiment of a direct fuel cellattached to a water generator 83 and a fuel (fuel solution) source 82.The water generator 83 is coupled to conduit 88, by conduits 89 and 90.Conduit 88 couples the fuel source 82 to the anode chamber 86. Operationof the water generator 83 is controlled by the operation of valve 91,which manages the flow of fuel or fuel solution into the water generator83 on conduit 89. This is alternative embodiment to that shown in FIG.2, which may also use any of the water generators of FIGS. 3-6.

FIG. 8 illustrates a direct oxidation fuel cell attached to a watergenerator 103 situated along a conduit 108 that couples an anode chamber106 to a fuel (fuel solution) source 102. Operation of the watergenerator 103 is controlled by the operation of valve 109, which managesthe flow of fuel or fuel solution through the water generator 103. Thisis a second alternative embodiment to that of FIG. 2, which may also useany of the water generators of FIGS. 3-6. Those skilled in the art willrecognize that it is possible, and it may be preferable to store anywater generated temporarily, and introduce said water to the fuelmixture at a later time.

FIGS. 3-6 show embodiments of a water generator that uses a flutedtubular membrane selectively coated or not coated with a catalyst. Thisis illustrative of preferred embodiments. Those skilled in the art willrecognize that one can substitute other carbonaceous fuels for methanoland aqueous solutions thereof, and use other catalysts and catalystmixtures instead of platinum or platinum-ruthenium mixtures, which maymore actively promote the direct oxidation of carbonaceous fuels in thepresence of oxygen. Those skilled in the art will further recognize thatany water generated using the methods or apparatuses set forth hereincan be distributed to more than one fuel cell, and still remain withinthe intent and scope of the invention. It will obvious to those skilledin the art that surfaces other than those described herein may be usedas a substrate in these reactions, and that water can be generated usingapparatuses that are of different configurations than those set forthherein, while remaining within the scope of the invention.

1. A water generator for a fuel cell system comprising: a housing; asubstrate; means for introducing oxygen into said housing; means forintroducing fuel or fuel solution into said housing; means for reactingsaid fuel or fuel solution with said oxygen to produce carbon dioxide,water and heat; means for mixing said water with said fuel to formdilute fuel; and means for removing said water from said watergenerator.
 2. A water generating assembly, comprising: a source ofcarbonaceous fuel; a source of oxygen; a catalyst; means for introducingcarbonaceous fuel from said source of carbonaceous fuel and means forintroducing oxygen from said source of oxygen in the presence of saidcatalyst to oxidize the fuel, producing carbon dioxide, water and heat.3. The water generating assembly as defined in claim 2 furthercomprising a control system for controlling the amount and introductionof at least one of fuel and oxygen to said catalyst.
 4. The watergenerating assembly as defined in claim 2 wherein said catalyst isdisposed on an element, which may include a substrate.
 5. The watergenerating assembly as defined in claim 4 wherein said element is asubstrate.
 6. The water generating assembly as defined in claim 2wherein said catalyst is disposed at one of the following: within achamber, in a chamber, and on an aspect of a chamber.
 7. The watergenerating assembly as defined in claim 2 used with an associated directoxidation fuel cell wherein said catalyst is disposed within the anodechamber of said fuel cell.
 8. The water generating assembly as definedin claim 2 used with an associated direct oxidation fuel cell whereinsaid catalyst is disposed within the cathode chamber of said fuel cell.9. The water generating assembly as defined in claim 2 wherein saidcarbonaceous fuel includes methanol.
 10. The water generating assemblyas defined in claim 5, wherein said substrate is a tubular substrate.11. The water generating assembly as defined in claim 10 wherein saidtubular substrate includes fluted walls.
 12. The water generatingassembly as defined in claim 10, wherein said catalyst is disposed on anexterior aspect of said tubular substrate, and said tubular substrate iscoupled with said source of fuel in such a manner that fuel isintroduced into an interior aspect of said tubular substrate wherebysome of said fuel passes from the interior aspect of said tubularsubstrate to said catalyst on the exterior aspect and the fuel reactswith oxygen, producing carbon dioxide, water and heat.
 13. The watergenerating assembly as defined in claim 12, wherein said catalyst isapplied to at least a first portion of said tubular substrate and atleast one second portion of the exterior aspect is exposed and iscatalyst free such that water produced on said exterior aspect passesback into the interior aspect of said tubular substrate.
 14. The watergenerating assembly as defined in claim 12, wherein said exterior aspectof said tubular substrate is enclosed with a liquid-impermeable,gas-permeable material forming an enclosure defining a space between theexterior aspect and the enclosure as a water generation and collectionarea.
 15. The water generating assembly as defined in claim 14, whereinsaid enclosure provides either a pressure or a concentration gradientacross the tubular substrate, and where carbon dioxide produced byoxidation of said fuel is released from the enclosure through theliquid-impermeable, gas-permeable material enclosing said tubularsubstrate.
 16. The water generating assembly as defined in claim 10,wherein said tubular substrate has said catalyst disposed on an interioraspect of said tubular substrate that is coupled with said source offuel in such a manner that fuel and oxygen are introduced to theinterior aspect of said tubular substrate whereby carbon dioxide, waterand heat are produced on the interior aspect of said tubular substrate.17. The water generating assembly as defined in claim 16 wherein saidtubular substrate is comprised of a gas-permeable, liquid-impermeablematerial such that water, heat and carbon dioxide are generated at theinterior aspect of said tubular substrate and carbon dioxide generatedpasses out through walls of said tubular substrate.
 18. The watergenerating assembly as defined in claim 17, wherein oxygen is introducedto the catalyst through said tubular substrate.
 19. The water generatingassembly as defined in claim 16, wherein at least one portion of saidtubular substrate is left uncatalyzed so that excess air and carbondioxide may pass through to an exterior aspect of said tubular substrateresulting in liquid water being collected, substantially gas-free on aninterior aspect of the gas-permeable, liquid-impermeable material.